Semiconductor electroabsorption modulators (EAMs) offer the advantages of low drive voltage, small form factor, and integratability with active optical elements. EAM-integrated lasers are widely used in metro-distance communication networks. EAMs are also key building blocks for highly integrated photonic circuits. The low drive voltage requirement of EAMs is especially promising for emerging high bit-rate (>100 Gb/s) communications, where the wide-band electrical amplification required for driving lithium niobate modulators (LNMs) is difficult to achieve.
In contrast to LNMs, which typically are operated using phase modulation combined with interferometric structures, EAMs have been used as single amplitude modulation elements. Considering the importance of phase shift keying (PSK) modulation, including quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM) in high bit-rate, high spectral-efficiency transmission, it would be desirable to use EAMs for a wider range of modulation formats other than amplitude modulation.